View source for Upper Carboniferous (Westphalian and Stephanian) and its classification, Bristol and Gloucester region

===Nailsea Syncline===
Coal workings here were abandoned between 1880 and 1890 because of heavily watered measures and the inferior quality of the coal, and there is little informa- tion about the succession. About 270&nbsp;m of shales and subordinate sandstones with 12 recorded coal seams are presumed to be Lower and Middle Coal Measures. Of the 12 seams only White’s Top (1.1&nbsp;m) and the Dog (0.9&nbsp;m) were mined to any extent. A maximum thickness of about 330&nbsp;m of sandstone, presumably Upper Coal Measures, rests on the Middle Coal Measures. Two seams are known here, but only one of these, Grace’s Seam (0.9&nbsp;m thick), was worked.

A short distance to the north of the main coalfield, Pennant Measures rest directly on Carboniferous Limestone with or without the intervention of thin Namurian quartzitic sandstone, thus testifying to strong sub-Namurian and sub-upper Westphalian unconformities.